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Volatiles, and Solid Earth Controls on the Habitable

The Earth is a layered, planetary body from the core to the , with , lithosphere and hydrosphere between. and are in abundance on the fertile surface we inhabit that overlies the barren, tracts of solid silicate mantle. This familiar arrangement has fundamentally compartmentalised the study of the Earth, with the hot interior frequently assumed to be dry. Such thinking has been reinforced by the practical difficulties of measuring the low abundances of volatiles within the Earth. Yet it has become increasingly apparent that the small amounts of volatile constituents can have a dominant effect on the behaviour of the mantle. As the largest reservoir on Earth, even small abundances of volatiles in the mantle can represent a major inventory of the planet’s volatiles. Thus the influence of volatile species on the operation of the mantle, which controls the storage and release of these volatiles to the surface represents Earth System Science on the grandest, most challenging scale. Advances in measurements of volatiles in nature and experiments, an understanding of their effects on rheology and an ability to compute these effects on the dynamics of the Earth now converge for the community to address this inter-connected system holistically. This Research Theme will thus quantitatively move geological thinking from a largely separate dry interior and wet exterior to a fully interacting model of the Earth. We will address the critical state of balance of the planet. Under what range of starting conditions can the Earth evolve to a planet with oceans and , and how robust is this system to perturbations? Can we lose our oceans and greenhouse-regulated atmosphere to the interior just as readily as we seem to have acquired them? Not only is the time ripe to tackle these zeroth order problems but there are the critical density of skills within the UK Geoscience community in order to efficiently address the interlinked components in this truly inter-disciplinary endeavour. 1. Introduction melts that produce continental would not Interactions between the mantle and the Earth's form. surface have dominated the evolution of the crust, • Carbonate sediment recycling back into the the oceans, and the atmosphere and those same mantle (via subduction) followed by emission processes control many aspects of the habitable via volcanic degassing is part of a long-term environment. The mantle is, by many orders of feedback modulating atmospheric CO2 levels magnitude, the largest reservoir of many volatiles that has been increasingly important since ~ on Earth (e.g., H2O, C, N, S), and volcanic 200 Ma – how was CO cycled in the Earth degassing and subduction ‘ingassing’ play a major 2 role in their cycles. The input and output of before this time? volatiles at plate boundaries provide major links • The link between mantle redox evolution and in the cycles of many important elements, large changes in surface chemistry, leads to including oceanic nutrients and climate-mediating major transitions such as the rise of species. Processes occurring at plate-boundaries atmospheric oxygen at 2.5 Ga and the underlie the generation of many mineral, transition from "iron rich, stagnant and low hydrocarbon, and geothermal resources, and play an important role in most volcanic and seismic oxygen" (ferruginous/euxinic) to hazards. Feedbacks among the mantle, the "oxygenated oceans" (oxic) oceans at ~0.5 lithosphere, the cryosphere, the hydrosphere, and Ga. the atmosphere exert long-term controls on Despite the planet’s self-regulation during many climate and the biosphere. Examples include: carbon-driven ‘hyperthermal’ crises in the past, it • By modulating mantle rheology, partial is unlikely to do so fast enough for humankind and redox state, volatiles influence given our current anthropogenic rates of carbon the operation and style of release to the atmosphere. An improved and plate tectonics (perhaps even playing a understanding of the role of volatiles in geodynamics, and especially the sensitive crucial role in its initiation). connections between the deep Earth, habitability • The composition of at subduction and the environment, is a vital component of our zones and ultimately the composition of the knowledge, both as an intellectual endeavour and continental crust depends on volatile budgets. in terms of managing our future relationship with Without water the silica-rich low density our planet.

1 2. The Research Programme (RP) The and been influenced by, redox (reduction- proposed RP, Volatiles, Geodynamics and Solid oxidation) reactions through geological time? Earth Controls on the Habitable Planet, will 3) How have the content and distribution of focus on the fundamental science of volatiles and volatiles influenced mantle convection and deep Earth processes, plate tectonics, melting and plate tectonics since the Earth formed? volcanism and their feedbacks to the surface Some of the key interplays relevant to these environment. This action specifically addresses themes are summarised in Figure 1. The scope ESS Theme Challenge 2: Understanding the long and delivery of each of these high-level themes is term development of the Earth and its addressed in turn in the following sections. 1 habitability which, amongst its goals, seeks to 3.1 How has cycling of volatiles between the “Improve knowledge and understanding of: how Earth’s surface and interior influenced the deep-earth processes influence the surface evolution of the habitable planet? environment; and the controls on subduction and mantle convection, melting and volcanism.” The importance of the mantle in determining the The goal of this RP is to understand the dynamic role of volatiles in mediating fundamental Earth processes that affect habitability, including mantle convection, plate tectonics, mantle melting and delivery, geohazards, and geothermal and ore-forming systems. Specifically the RP will aim to define and understand the controls on the volatile flows and budgets in the mantle, and their feedbacks with mantle behaviour, through well- defined programmes including observations on active geological systems (subduction zones, mantle plumes and spreading centres) and palaeo- analogues, together with closely-aligned laboratory experiments and computer simulations, and coupled geodynamic modelling and seismic imaging. It is expected that successful bids to this Figure 1. Schematic summary of volatile cycling programme will combine scientists from a wide and influences – which should be considered in the range of sub-disciplines within Earth Sciences, critical context of time, since the magnitude and and that their chosen areas of study will be type of influence will have varied over the 4.5 Ga of justified on the grounds of the relevance of those Earth history. areas to global Earth System Science problems. It ability of the planetary surface to support life is through truly interdisciplinary work that depends on the mass and composition of volatiles innovation will come; the RP will act as a catalyst initially available in the mantle, and the exchange to initiate work between communities of scientists fluxes of volatiles into and out of the surface that do not necessarily traditionally work together. reservoirs. The interplay between the surface 3.The Science and Delivery reservoir and deep Earth volatile budgets has evolved over geological time. Thus our The programme will require a highly understanding of volatile cycling between the collaborative and interdisciplinary approach deep Earth and the surface breaks down into four involving expertise across a wide range of fields related questions: including , geochemistry, mineral physics and , and involving fieldwork, (i) What was the Earth’s initial volatile laboratory studies and computer modelling. It is inventory? envisaged that the program will involve delivery Our understanding of the origin of volatiles within via competitive consortium-scale (or larger) the planet has evolved dramatically in the last few proposal(s) to address and integrate the following years, linking the origin of mantle volatiles to three interlinked major themes: those brought to the Earth trapped in meteorites2. 1) How has cycling of volatiles between the There is evidence from intraplate volcanic Earth’s surface and interior influenced the systems that the mantle also contains volatiles 3 evolution of the habitable planet? from the earliest Solar Nebula . These initial 2) How have volatile flows both within the solid volatiles have been complemented by recycled 4. Establishing the initial volatile Earth and its surface reservoirs controlled, surface volatiles

2 element inventory of the mantle provides a key wedge, triggering melting and emerging boundary condition for any assessment of the ultimately in arc magmas, while others are mantle volatile output to the surface. recycled into the mantle. The efficiency of Delivery: The grand challenge is to resolve the recycling and its long-term variability are different contributions to the major volatile unknown, but the extent to which volatiles are species from accretionary or recycled sources. released or retained by subducting slabs is thought This can now be done using and integrating key to be controlled primarily by the thermal structure 5 geochemical tracers such as noble , halogens of subduction zones . and incompatible elements. These geochemical Delivery: Addressing this question will require observables, and our understanding of the wide interactions between petrologists, fundamental controls on their transport, geochemists, structural geologists, seismologists partitioning and storage, provide the starting point and geodynamic modellers. Examining the for dynamic models that incorporate chemical products of arc magmatism and metamorphic tracking. The models in turn allow us to assess the rocks at exhumed subduction zones back through temporal impact of recycling and degassing on the time would allow us to understand the changes in major element volatile concentrations, isotopic arc volatile budgets mediated by recycling of compositions, and their spatial variance in the surface-derived components, melting and mantle. changing thermal regime. Seismic imaging of (ii) How have volatile reservoirs changed subduction zones (most likely involving both through time? active and passive source methods) can be combined with petrological models to provide Once the initial volatile boundary conditions have constraints on the distribution of volatiles in the been established it is essential to develop an system, and allow the estimation of input fluxes. understanding of how volatile reservoirs Observations of magmatism and seismicity can subsequently evolve and interact over time. This also be compared to the predicted volatile is a key question since it constrains fluxes among distribution. reservoirs, and will allow direct comparison of Earth with other planetary bodies. (iv) How is volatile cycling affected during periods of major perturbations in the Deep Earth Delivery: We are well positioned to address this system? challenge using state-of-the-art approaches. Precise high-spatial resolution chemical analysis One of the best ways of understanding how a of trace constituents (e.g., volatile elements, given system works is to disturb it and see how it incompatible elements and redox-sensitive behaves. Will it revert to some preferred “steady species) in melt inclusions, undegassed magmatic state” or will it cross a tipping point? There are samples and mantle xenolith minerals can be used periods in Earth History when dramatic and to define past and present volatile inventories. relatively short-lived changes in the Earth System Laboratory partitioning measurements using have occurred that had a clear mantle-driven natural samples and experimental products are component. This has the particular advantage of essential for constraining fluxes between being able to identify and assess the significance reservoirs, and for understanding the mineral- of major feedback loops. scale reactions that control volatile release in the Delivery: The stratigraphic record across suitable solid Earth. Inverting the compositions of ancient events provides quantitative detail about the rocks can be used to constrain changing source timescale, volatile composition and mass of volatile contents. Data mining will provide a material involved in these global events. This critical complement to new studies. Modelling work may challenge the current surface-centric studies of different types and complexity will view that the Earth system can be understood complement these data. purely in terms of carbon cycling in crustal rocks. (iii) What controls the volatile budget of a In the Cretaceous, for instance, there was a major subduction zone in space and time? period of Deep-Earth-triggered large volume 6 As the Earth’s primary “valve” controlling the magmatism , magnetic quiescence (no reversals), long-term input and output of volatiles, it is increased spreading, ocean basin flooding and perhaps surprising that our understanding and climate warming, with consequent seafloor quantification of processes at subduction zones is anoxia, and subduction of anoxic sediments. relatively poor. Volatile-bearing lithosphere is Other examples include the Great Oxidation demonstrably returned to the mantle. Some Event (2.5 Ga), Snowball Earth Recovery (0.65 volatiles are released into the overlying mantle Ga) and the Permo-Triassic Siberian traps and mass extinction (250 Ma). The interrelationships

3 among volatile outgassing, climate, sea level and corresponding speciation and potential budget of subduction zone magmatism predicted from volatile elements. For example, models for the global geodynamic models of volatile exchange speciation of ‘simple’ C-O-H-S fluids as a between mantle and surface reservoirs could be function of oxygen fugacity are calculated on the directly tested in such cases by combinations of basis of estimates of fluid targeted field observation and laboratory analysis. fugacities, which are founded upon molecular 15 3.2 How have volatile flows both within the dynamics calculations of pure fluid properties . solid Earth and its surface reservoirs There are virtually no high- and - controlled, and been influenced by, redox experimental data to confirm the (reduction-oxidation) reactions through simulated properties even in simple systems; geological time? gross extrapolations are necessary to model deep mantle conditions, and information on critical S- The form and abundance of volatile elements that are exchanged between the surface and deep Earth bearing systems are lacking. Sulphur is a key 7 element in redox reactions due to its highly reservoirs depends critically on oxygen fugacity . variable oxidation state and capacity for electron This is because the speciation of volatiles, and 6+ 2- transfer (S to S ), and may play a critical role in therefore the phases they can exist in and their oxidative transfer from subducted slab to the migration through the mantle and exchange at the mantle wedge and in regulating the redox state of surface, are regulated by oxidation-reduction mantle-derived magmas 16. Volatile speciation and reactions. For example, the redox state of the fluid properties as a function of oxygen fugacity mantle determines whether carbon is present in its in the more complex silicate systems that oxidized and potentially mobile form as carbonate comprise the mantle are currently not available. or carbonatite melt (which lower the mantle We envisage activities within this part of the RP solidus by several hundred degrees), or whether it might be organised around the following is present in its reduced and immobile form as fundamental questions: graphite or (which do not affect melting )8. The proto-atmosphere (i) What are the boundary conditions for the composition and the emergence of a habitable redox state of the early mantle? surface was intrinsically linked to the early mantle Endeavours in this field are fundamentally linked redox state as a consequence of early atmospheric to our understanding of the origin and distribution outgassing9. Redox sensitive volatile elements of volatiles in the early Earth (see section 3.1). such as carbon and sulphur can potentially buffer Key topics that need to be addressed include oxygen fugacity in the mantle or in magmas that determining the likely oxygen fugacity of 17 degas to the surface10, and it is clear that they accretionary materials , and the effects of early must adjust to changes in oxygen fugacity dictated magma ocean differentiation, core formation and the moon-forming impact on the mantle’s volatile by mineral equilibria involving elements with 18 multiple valence states, especially iron through inventory and initial redox state . Fe2+-Fe3+ equilibria11. The redox state of deep Delivery: The main approaches that might be Earth reservoirs would have been established applied to this problem include high-pressure initially after core formation, but would have experimental studies, geochemical measurements evolved with time by processes of internal of natural samples, and modelling. For example, differentiation and through the two-way link with the impact of core formation and the the surface12. The potential for the mantle to crystallisation of the magma ocean on mantle become oxidized by subduction input has been volatile contents and redox state can be studied recognized13, and there is now compelling through high-pressure experiments that constrain evidence linking subducted slab materials to how volatile elements partition among mantle and core phases at conditions corresponding to the oxidation in the mantle wedge beneath 19 subduction-zone volcanoes14. early magma ocean stage . Investigation of primitive samples together with mantle- Even though the importance of redox equilibria derived samples using novel isotope tracers in for mantle-surface evolution has long been radiogenic and stable isotope systems that have recognized, significant knowledge gaps exist in recently been developed can place important new terms of identifying and quantifying the roles that constraints on initial volatile contents in Earth and redox equilibria play in deep Earth volatile mechanism of volatile differentiation20. reservoirs, and how they relate to the surface (ii) What is the speciation of volatiles in the environment. Currently we lack the required mantle as a function of redox state? information to model the redox state throughout In order to develop models for the deep Earth Earth’s interior adequately, and therefore the control on the global volatile cycle, we need to 4 know the chemical speciation of volatiles in the both in the chemistry of material recycled from mantle as a function of redox state. Specifically the Earth’s surface into the deep mantle by plate we need to know the species that are present in C- tectonics32. Surface-derived volatile species can O-H-S fluids that are in equilibrium with mantle potentially be identified in deep-Earth reservoirs, lithologies as a function of depth, temperature and for example through studies of and their oxygen fugacity21. This information will allow us inclusions, and they can be linked to both the to place important constraints on how mantle redox chemistry of recycled material and to redox state and volatile speciation in the mantle geodynamic processes involved in crustal affected the composition of the proto-atmosphere, recycling33. and how the mantle redox state may have evolved 3.3 How have the content and distribution of with time and interacted with the evolving volatiles influenced mantle convection and atmosphere through surface magmatism. plate tectonics since the Earth formed? Delivery: This topic requires a coordinated Volatiles may weaken the rheology of mantle program of experimental geochemistry and first minerals by as much as an order of magnitude or principles calculations, coupled with constraints more34. As the mantle volatile composition on secular variations in mantle redox state evolves through volatile loss to the planet’s (discussed below in question iii). Ab initio surface and subduction of volatiles back into the calculations coupled with high-pressure and – mantle system, the feedback into rheology may temperature experiments can be used to determine change the convective style and vigour with volatile element stability and partitioning among 22 which the mantle convects and affect the style of mantle phases (see also section 3.1.ii), volatile 35 plate tectonics . A critical feedback between element solubilities in deep mantle and core volatile content and rheology may aid in plate- phases23, the effects of volatiles on mantle boundary formation, as well as result in mantle melting24, and volatile speciation in melts and regions with higher water content flowing faster fluids25, all as a function of redox state. than drier regions promoting shear decoupling of (iii) How does recycling of volatiles change the water poor regions from overall mantle flow. mantle redox state through time? Another potential result is that the convective While we know that the redox state of the planet’s overturn rate and heat transport out of the mantle surface has varied significantly over geological as a whole may see a secular rise as the mantle time, our understanding of the secular and spatial becomes more hydrated. variations in mantle redox remains in its infancy. Existing proxies based on Fe3+ mineral The combination of recent advances in numerical equilibria26, vanadium partitioning27 and the stable simulations and a fundamental understanding of isotope signatures of redox sensitive elements the effect of water on rheology, if brought such as iron28 and vanadium29 provide some together, have the real prospect of a constraints on secular variations in mantle transformative change in our understanding of oxidation state, but the existing data coverage is convection within the Earth’s mantle, a new restricted. Recent progress in using synchrotron- insight into how our deep planet works, and how based XANES measurements to measure the it controls or moderates planetary habitability. valence state of redox sensitive elements in Advances will be even greater if we add the mantle samples directly is a promising way volatile boundary conditions and observational forward30, especially with world-class facilities constraints provided by the carefully-planned available at the Diamond Light Source geochemical campaign outlined above. Indeed, synchrotron. Such information is crucial in our understanding of mantle volatile flux to the evaluating whether the mantle controlled or surface, and its role in controlling planetary responded to surface redox changes such as the habitability, is only as good as our understanding great oxidation event. of volatile return into the mantle and the feedback effect this has on mantle geodynamics over time. Delivery: State-of-the-art observations such as In addressing this, there are several key questions: synchrotron-based X-ray absorption techniques on mantle derived samples can be used to explore (i) How can we build a complete understanding spatial and secular variations in the redox state of of how volatile content and heterogeneity control magmatic and mantle samples from the Archean mantle rheology? to the Phanerozoic31, providing much needed Although we know that small variations in the information about coupling of deep mantle redox water content of mantle minerals play a processes to the surface. This information can be fundamental role in determining their , linked with geochronological constraints to quantifying this has proven difficult with provide information about secular variations in estimates ranging from less than an order of 5 magnitude weakening to several orders of elements over time by tracking radioelements magnitude. This is a particular problem at higher such as U and K. The key advantage of this pressure and temperature, but also in complex approach is in providing a three dimensional mineral assemblages where the partitioning of understanding though time of volatile, trace water between different phases, relative phase element and isotope distribution - all within the proportions and the connectivity of different constraints imposed by our understanding of the phases must all be considered. fluid dynamics. In exactly the same way as the Delivery: Advances in computational techniques geophysical constraints of seismic imaging and have now made it possible to use first principles mineral physics, observed volatile and trace techniques at the atomic scale to obtain the element distribution and observed scale of rheology of mantle minerals throughout the isotopic heterogeneity provide the key conditions mantle for both diffusion creep36 and dislocation that the models must match to gain confidence in creep37, and multiscale physics can then be their robustness and ability to define volatile flux utilized to apply these single results to out of and into the mantle. polycrystalline rocks38. Improvements in 4. Why Theme Action mode of laboratory techniques are allowing us to measure rheological properties experimentally under upper funding is necessary mantle conditions39, and plans to extend these to This proposed RP will focus on the fundamental the lower mantle using diamond anvil technology science of volatiles and deep-Earth processes, are underway. plate tectonics, melting and volcanism and their feedbacks to the surface environment. Although ii) How can the predicted geophysical and the research outcomes will be relevant to other geochemical signatures of a dynamic feedback themes such as Natural Hazards (volcanoes and between volatile content, mantle rheology and earthquakes), Sustainable Use of Natural convection distinguish mantle evolution resources (mineral and hydrocarbon resources) scenarios? and other components of the ESS theme (oceanic Numerical simulations of mantle convection may and atmospheric composition, paleo-climate), the be three dimensional, two dimensional or focus of this action on fundamental science means sophisticated box models – depending on the the programme is better delivered as an exclusive application and focus of the hypothesis to be ESS programme, rather than as a joint action with tested. The degree of UK expertise and computing those themes. Volatiles, Geodynamics and Solid power now available enables, for example, Earth controls on the Habitable Planet is models to work at Earth-like convective vigour appropriate for a RP for two main reasons: (i) the and in providing global simulations using need to develop large interdisciplinary teams to complex rheology in spherical geometry. Both tackle strategically important science objectives; seismic imaging and mineral physics have a key (ii) the legacy it will leave in terms of the UK role to play in testing model confidence: For solid- and deep-Earth communities. example, fluid dynamical models are being used (i) The need to develop large interdisciplinary to identify the mantle conditions that influence the 40 teams to tackle strategically important science results of seismic tomography imaging . This objectives. harnesses recent developments in both inversion technologies and waveform propagation The opportunity presented by a theme action for a modelling. Further cross-disciplinary constraints “large targeted investment where coordination and on how seismic parameters relate to physical integration are essential” is precisely what is conditions are being supplied by molecular needed to deliver research “broader in scope than dynamics and mineral physics41. A combination is normally achievable via responsive mode of geodynamic flow models and mineral physics funding”. The key to a step change in our are being used to predict the large-scale understanding is effective integration. development of mineral fabrics, which can be Cross-disciplinary work to date addressing these compared with observations of seismic science problems has been in the most part bi- 41 anisotropy . lateral43. It is now very apparent that to make a Delivery: Numerical modelling approaches have significant advance in this field we need a had for some time the capacity to track coordinated program that brings together and geochemical information42. These types of model exploits the recent advances across laboratory not only return concentration information through experiments and geochemistry, seismic the effects of melting or degassing, but are also observation, mineral physics, molecular able to follow the isotopic change of different dynamical simulations and fluid dynamics.

6 (ii) The legacy it will leave in terms of the UK the form of volatiles in these super-deep solid and deep Earth communities. reservoirs. The UK is an international leader A RP focussed on Volatiles, Geodynamics and in ab initio simulation of phase equilibria and Solid Earth controls on the Habitable Planet, by material properties at the extreme conditions 46 its explicit co-ordination, will bring together the of planetary interiors . UK Deep Earth community and form links that • High P-T Experimental Geochemistry and will far outlast the RP itself. The delivery of the Mineral Physics. High P-T experimental required interdisciplinary science in the RP will investigations at conditions from the crust to provide an excellent training and development the core are essential for understanding opportunity for graduate students and post- volatile speciation, phase equilibria, doctoral researchers ensuring a legacy of UK partitioning, and mobility. Mineral physics scientific leaders in this area. Critical in this and experimental petrology are underpinned legacy is establishing a strong network of by at least five world-class University interdisciplinary science that will establish a laboratories, further theoretical groups and culture of resource, training and infrastructure national facilities like the Diamond Light sharing that will change the way this area of Source. science will be delivered in the UK and further • Fluid Dynamical Modelling: Quantifying enhance its international competitiveness. volatile exchange between deep reservoirs To ensure this legacy further we suggest that the depends on the mechanism and rates of RP budget should explicitly provide funding for mantle and lithosphere flow. The UK is frequent joint workshops for the students, PDRAs amongst the leaders in developing places also for attendance by scientists not funded simulations, which include non-linear within the consortia. viscosity, the effects of phase transitions and, increasingly, chemistry47. The geodynamics 5. UK Contribution and Capability community is underpinned by NERC’s The UK is world-leading in many of the scientific advanced computing facilities. communities needed to deliver conceptual step changes in these areas. The scoping phase of this RP has shown how stimulating bringing these different communities together can be and the time is ripe to build upon this momentum. To deliver innovation in this area will require groups working in areas such as volcanology, geodynamics, , mineral physics, , experimental petrology and igneous geochemistry to work together as well as engaging with the wider NERC community when communicating their science. Some specific areas are discussed in more detail below (and summarised in Figure 2):

• Seismic Imaging: Seismology provides the most direct observations of large-scale mantle properties. UK groups play a leading role in

advancing global seismic tomography and are at the forefront of seismic imaging of anisotropy at a range of scales44 – critical for

testing models of the interaction of volatiles and geodynamics. There is also a wealth of experience in crustal-scale active source seismology. • Computational Mineral Physics: Calculating the stability and physical properties of Figure 2. volatile-bearing materials at deep mantle and Summary of relevant UK strength and facilities. core conditions is critical for understanding

7

proposed initiative. Some examples are given • Trace Element and Isotope Geochemistry: below: Chemical and isotopic analyses are central to • New developments in geochemical analyses: tracking the geochemical and geodynamic a trend towards progressively smaller sample processes that moderate volatile budgets and sizes, precisions and length scales. The provide temporal constraints. The UK has an development of ablation and mechanical extensive NERC-funded state of the art micro-sampling techniques, alongside equipment-base. Over eight UK groups lead multicollector mass spectrometry and more the development and application of novel sensitive detection techniques has enabled the 48 tracers and microanalytical techniques . UK community to be among the leaders in • Geochemistry: Volcanic analysing samples within petrological outgassing plays a key role in the interplay contexts50. This has enabled us to examine and the planet’s surface environment both in mineral zoning and use this to back out terms of long-term stability and short-term petrogenetic processes from core-rim perturbations. Over seven UK groups play a profiles51, and to analyse melt inclusions to world-leading role driving this scientific 52 49 determine melt evolution and particularly field . volatile budgets. Equally important has been • NERC and RCUK Facilities: Central to a the step improvement in mass spectrometry successful deep Earth volatile Programme are technology with the advent of multi-collector the world-class national analytical and systems. For example, within the last few computational facilities, including the years we have seen an improvement in the Diamond Light Source, NIGL, SUERC, the precision of some noble gas isotope ratio Edinburgh Ion Microprobe Facility, and the determinations by up to a factor of fifty53. HECTOR and ARCHER computational • Combining computer modelling and facilities. experiments to probe volatile partitioning 6. Timeliness between different mantle phases. Ab initio The strongest justifications for timeliness lie in calculations coupled with high-PT the previous section. The UK community has an experiments using state-of-the-art multi-anvil assembly of expertise and facilities, and a track and techniques provide a record of inspiration and innovation, that together powerful complementary approach. Recently are poised to make a difference in this field. The developed state of the art internally and UK is already at the cutting edge in many of the externally-heated diamond anvil cell disciplines that focus on Deep Earth problems, techniques coupled with laboratory-based and and the goal of this action, is to instigate synchrotron-based spectroscopic methods transformative science by bringing these now permit in situ measurements of fluid communities together. There are also key recent speciation, and allow investigation of volatile- technological advances and international bearing phase equilibria to core conditions. programs that naturally link into the core science Recently developed synchrotron X-ray of this action and further enhance the timeliness microtomography techniques coupled with of the proposed RP. high-pressure multi-anvil apparatus permit direct measurement of fluid volumes, and (i) Recent technological advances multi-anvil techniques combined with micro- Technical advances, such as in seismic analysis (e.g. SIMS, FTIR) permit interpretation, modelling capability and measurement of volatile partitioning among geochemical analysis techniques, are contributing mantle phases. Thermodynamic data such as to improved acquisition and analysis of enthalpies, chemical potentials, and volumes geophysical and geochemical data. Rich new of mixing can now all be obtained via ab datasets are now developing that offer an initio molecular dynamics techniques and fit opportunity for a major synthesis effort within this to equations of state. These equations of state proposed RP. This will allow the science to take a can then be used to predict volatile major conceptual step forward, moving from partitioning between different mantle phases developing hypotheses to tackling major research and at different conditions, which can be questions with more effective interdisciplinary directly verifiable and supplemented by high- research amongst the core disciplines. The UK is pressure experimentation. This playing a major role in the exploitation of these complementary approach between experiment developments and is well placed to spearhead this and theory is key to providing results with the

8 highest possible degree of confidence. clear synergies with the proposed RP. The NERC's investment in the new national high DCO welcomes this interaction and the performance computer to be installed in 2013 scoping workshop was attended by the DCO (ARCHER) is a timely development in UK Director, Craig Schiffries. computational capability and will make these • GeoPRISMS:The US NSF is in its second calculations possible. iteration of thematic funding (“GeoPRISMS • Computer models of convection: handling (http://geoprisms.org/ )following on from large variations in strain and the feedback ”Margins”, 2000-2010) with a major focus between chemistry and rheology. It is now on subduction zones, including cycling of possible to model, from first principles and at volatiles. Support and offers of the atomic scale, the rheology of lower mantle collaboration have already been offered by the minerals. Advances in experimental methods GeoPRISMS leadership for this RP. Similar allow the rheology of Earth materials to be to the DCO this program offers access to the measured directly for large volumes of sample networking opportunities, collaborative under the temperature and pressure conditions interactions and data outputs of a major and of the , and lowermost mantle complementary international effort. conditions will soon be obtainable. However, GeoPRISMS was represented by Katie Kelley uncertainties remain in the theory of the at the scoping workshop. deformation of poly-phase polycrystalline • Computational Infrastructure in composites (rocks) and how to best describe Geodynamics (CIG): This NSF-funded, their deformation within larger scale models membership-led organisation supports and of mantle convection. Mantle convection promotes Earth science by developing and models and computational power have maintaining software for computational recently advanced to the point where they are geophysics (http://geodynamics.org/ ) UK be able to incorporate non-linear and material universities including Bristol, Cardiff and dependent rheologies in global scale models UCL are foreign affiliate members of CIG. thus allowing to test the implications of Collaborating with this organisation will experimentally and numerically constrained enable the broad impact of software flow laws. developed and enhanced by activity in the RP. • Driving the limits of seismic imaging: Louise Kellogg represented CIG at the global full waveform tomography. The (geodynamics) scoping workshop. development of adjoint inversion and 7. Impact waveform modelling techniques and the meteoric rise of available computing power is The fundamental impact of this RP will be to driving a revolution in full waveform inspire and inform both the science community tomography. It is now possible to make global and public alike. Examples of this outside the models to match large global datasets at long NERC arena are seen for example through periods. Improvements over the next few improvements in understanding the years will see the frequency being driven via remote missions such as the Cassini-Huygens higher, improving not only the resolution of probe, the upcoming ROSETTA mission to a the models but also the range of parameters , and even the Google Lunar-X prize. The which can be robustly determined. obvious immediate benefits include bringing together UK researchers at the forefront of this (ii) Complementary international programmes field, training a new generation of highly skilled The UK has ongoing synergies with relevant and interdisciplinary scientists, and maximising international programmes including: use of recent NERC investment in the world-class • The International Deep Carbon UK scientific infrastructure. We also expect the Observatory (DCO): This program, is continued development of new analytical and managed through the auspices of the Carnegie computational methods will require input from Institution of Washington (USA) UK industry and enterprise. In particular (https://dco.gl.ciw.edu/), and is a interactions with the strong UK analytical “multidisciplinary, international initiative equipment industry base will benefit from a dedicated to achieving a transformational buoyant scientific community in this area understanding of Earth's deep carbon cycle”. allowing, for example, UK industry to continue to The DCO provides substantial support and lead the world in supplying state of the art mass access to the international community and has spectrometers.

9 8. Indicative budget PDRA positions in each of Geochemistry and Geophysics would support the focussed research Core person hours: We envision a roughly equal effort of the specialist groups. split in the budget between Geophysics and Geochemistry. We have used a notional £100k The total effort of the 3- and 5-year postdoctoral average cost per postdoc year to represent typical fellows would be about 70 person years (see FEC costs that include the PDRA’s time, a example resource chart in Appendix 1), costing proportional amount of time spent on the project £6.4million by a senior permanent academic, travel Training: PhD student training costs (fieldwork, conferences, twice yearly TAP group approximately £20k/year, with each student meetings, local meetings), and laboratory costs requiring 3.5 years to complete. 18 PhD students (including small equipment). This effort will (parity in numbers with the PDRAs) would cost need about 18 PDRAs. £1.26 million. 5 × 5-year Senior PDRAs (could be funded Facilities:Use of national facilities (including ship through a special fellowship round) would time, computing, Diamond, NIGL, EIMF, provide the experience and continuity essential for SUERC) could range from £1-3million depending a 5-year program. These would ideally be on need. We budget here for the average value of assigned to each of the key areas in Geochemistry £2million. and Geophysics to supervise and coordinate Total TAP Budget: (Indicative) = £9.66million across disciplines. An additional 7-8 × 3-year

10 Appendix 1: Example resource chart

Postdocs +Academic + Lab costs at FEC @ £100K per year £6.4 million = 64 Postdoc

11 Appendix 2. References

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Appendix 3. Le tter of support from GeoPRISMS

RICE

DEPARTMENT OF EARTH SCIENCE WIESS SCHOOL OF NATURAL SCIENCES

May 29, 2012

Professor Jon Davidson and colleagues c/o Dept of Earth Sciences University of Durham Durham DH1 3LE

United Kingdom

Dear Professor Davidson,

The GeoPRISMS Steering and Oversight Committee (GSOC), on behalf of the GeoPRISMS community, is pleased to learn of your proposal for a NERC Theme Action on Volatiles, Geodynamics and Solid Earth Controls on the Habitable Planet. Your proposed objectives of assessing volatile controls on Deep Earth processes such as mantle convection, growth of the crust, and subduction zone dynamics (through seismicity, magmatic outputs, deposition of resources, etc.) clearly have an important relationship to surface processes and our planetary “habitability.” These issues are highly compatible and complementary with the mission of the NSF GeoPRISMS Program (http://www.geoprisms.org). GeoPRISMS seeks an integrated understanding of volatile fluxes and of the material cycling and deformation driven by subduction processes as part of its Subduction Cycles and Deformation (SCD) Initiative.

Therefore, on behalf of the GeoPRISMS community and the GSOC, I offer full support of your proposal to NERC. GeoPRISMS clearly recognizes the need to link and integrate efforts with international partners, and values enhanced collaboration between the UK and GeoPRISMS communities. Moreover, we particularly recognize such international cooperation as a key means to achieve GeoPRISMS program goals, which by their nature span scientific disciplines and political borders, and further anticipate that our community support will similarly aid in the achievement of your own program objectives.

Sincerely,

Julia K. Morgan Professor, GeoPRISMS Chair E-mail: [email protected] Tel: 713-348-6330

RICE UNIVERSITY • DEPARTMENT OF EARTH SCIENCE-MS 126 • P.O. BOX 1892 • HOUSTON, TEXAS 77251-1892 6100 MAIN STREET • HOUSTON, TEXAS 77005-1892 • PHONE: 713-348-4880 • FAX: 713-348-5214 • E-MAIL: [email protected]

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